1. Field of the Invention
The present invention relates to an axle driving unit suitable for use with a rear-discharge lawn tractor having a mower located beneath the body of the tractor between the front and rear wheels.
2. Related Art
U.S. Pat. No. 3,969,876 discloses a conventional lawn tractor having a rear discharge system, which has a mower driven by a prime mover mounted on it, and a leaf blower loaded on the rear portion of the tractor. The rear discharge system disposes a chute, for discharging lawn grass cut by the mower, longitudinally between the left and right rear wheels. The rear discharge system has no projection to the outside of the body of the tractor. The cut lawn grass is discharged directly rearwardly of the tractor. This has the advantage of eliminating equipment, such as an auxiliary suction fan.
However, because the space between the left and right rear wheels is very narrow, it is very difficult to laterally juxtapose therebetween the cut grass chute and an axle driving apparatus. As disclosed in U.S. Pat. No. 3,969,876, a hydraulic stepless speed change transmission and a differential gear constituting the axle driving unit are separated and are housed in separate housings. The differential gear is disposed in the narrow space between the wheels, and the transmission is disposed at another position on the body of the tractor. The output shaft of the hydraulic stepless speed change transmission and differential gear are connected by a chain belt mechanism. Accordingly, the axle driving unit has the disadvantages of a high manufacturing cost and a long assembly time. Also, since one axle, through which the cut grass chute passes, is much longer than the other axle, this design has the further disadvantage that the one longer axle is easy to deflect. Accordingly, the life span of a bearing for the one longer axle provided at the differential gear is reduced.
An axle driving unit which houses in a common housing a hydraulic stepless speed change transmission and a differential gear for differentially connecting a pair of axles and integrates them is well-known, as disclosed in, for example, U.S. Pat. No. 4,914,907 and No. 4,932,209. In these patents, the transmission comprises a combination of a variable displacement type hydraulic pump and a fixed displacement hydraulic motor. The hydraulic pump and motor are mounted side by side and longitudinally of the axle with respect to an L-like-shaped center section, whereby the entire axle driving unit is larger-in width longitudinally of the axle. Hence, the axle driving unit of this design interferes with the chute of a lawn tractor which has a rear discharge system. As a result, the chute cannot be disposed between the left and right rear wheels.
The axle driving unit of the present invention is constructed so that a first shorter axle that mounts a first driving wheel, and a second longer axle that mounts a second driving wheel are supported by a housing provided on a body frame. The housing is attached to the tractor body frame so that it is eccentric or offset to be in proximity to the first driving wheel. The housing is provided with an enlarged region extending forward at approximately a right angle with respect to the axles. A hydraulic stepless speed change transmission is provided in the enlarged region. As a result, the axle driving unit of the present invention can be easily disposed laterally of (or to the side of) the chute of a lawn tractor of the rear discharge type.
In order to improve the operating efficiency of the hydraulic stepless speed change transmission, it is desirable to construct the transmission so that it is a hydraulic stepless system fluidly connecting the hydraulic pump and hydraulic motor to each other. In this case, the hydraulic pump can be disposed in the enlarged region, smaller in width and spaced apart from the axle, and the hydraulic motor can be disposed in proximity to the axle.
In the enlarged region are provided a pump mounting surface and a motor mounting surface disposed substantially perpendicular or rectangular with respect to each other for mounting the hydraulic pump and hydraulic motor. It is preferable that the hydraulic pump is mounted onto the pump mounting surface so that an input shaft connected to the hydraulic pump is oriented approximately vertically with respect to the axles, and the hydraulic motor is mounted onto the motor mounting surface so that an output shaft connected to the hydraulic motor is oriented approximately horizontally with respect to the axles. In a lawn tractor that includes a prime mover having a vertical crankshaft, the input shaft of the transmission can be connected therewith by use of a simple belt transmitting mechanism. The output shaft of the transmission can be connected with the axle by use of an inexpensive spur gear having a low manufacturing cost.
Bearing means are provided in the housing for supporting the first and second axles. A pair of bearing holding portions for supporting distal portions of the first and second axles define the width of the housing to be smaller than the length of the housing including the enlarged region. As a result, the enlarged region is elongated so that the chute can have as large a cross-sectional area as possible.
It is desirable that the second longer axle be supported at an intermediate portion thereof by a bearing device provided on the tractor body frame. As a result, the second longer axle is stably supported. It is also desirable that the second axle be composed of at least two axle parts separably connected with each other through a coupling. Hence, the axle driving unit becomes superior in assembly efficiency and transformation efficiency. The axle to which the other (first) driving wheel is mounted is stably supported by a bearing device provided on the tractor body frame.
The above and further objects and novel features of the invention will more fully appear from the following detailed description when the same is read in connection with the accompanying drawings.